One bone and ancient DNA move two family histories further back
A birth line in one bone pushes live birth in the mammal lineage back 90 million years, while Yorkshire DNA traces descent from mother to daughter across nine Iron Age generations.
Science··Midday
A birth line in one bone pushes live birth back 90 million years
A growth ring in the bone of Chiniquodon theotonicus, a dog-sized animal that lived in Argentina about 236 million years ago, points to live birth rather than hatching. Leandro Gaetano and colleagues report the finding in Frontiers in Mammal Science; if it holds, live birth in the mammal lineage began 90 million to 95 million years earlier than thought. The team measured the neonatal line, a disorganised band that forms when growth accelerates just after birth. From limb-bone size they estimate about 12 kg at death and about 1.7 kg at birth, roughly 14 per cent of adult mass. They set that ratio against 1,869 living mammal species, 2,619 non-avian reptiles and 782 birds. In reptiles of comparable weight, hatchlings run 0.1–0.6 per cent of adult mass, in birds 1.3–4.5 per cent, while in mammals the figure can reach 20 per cent. Emily Rayfield of the University of Bristol, who was not involved, calls it short of proof but consistent with live birth. Gaetano notes that in the arid, predator-heavy aftermath of the end-Permian extinction an egg cannot flee and a newborn can.[1]
Yorkshire DNA shows descent ran mother to daughter for nine generations
On a much nearer family line, Ian Armit of the University of York and colleagues sequenced the DNA of about 500 individuals from the Arras culture in pre-Roman Britain. Maternal lines can be traced for nine generations, while fathers are often absent from the burial ground. The work points to repeated unions between two maternal clans, and cemetery layout reinforces mother-to-daughter descent. About 400 samples come from Wetwang Slack in the East Riding of Yorkshire, the largest known Iron Age burial ground in Britain, most active between the fourth and second centuries BC. Most women buried there had close relatives such as a mother buried there too, which was rarer for men; in a few cases a man from one site is seen to have fathered children at another. At least 12 women had children by more than one man, which the team writes could reflect serial monogamy or polyandry in a female-line-centred structure. People of the same maternal lineage avoided having children together, while the three chariot burials stand outside that pattern through recurrent close-kin unions. Rachel Pope of the University of Liverpool considers the finding capable of changing how the Iron Age is understood. Matrilocality was not universal: other DNA studies point the other way for south-east England.[2]
Two lines of evidence reread descent as older and more female-centred
One bone and one cemetery DNA set move family history on two scales. In the Chiniquodon case the neonatal line and an estimated 14 per cent of adult mass at birth pull live birth 90 million to 95 million years earlier; Rayfield calls that short of proof but consistent with live birth. In the Arras sample maternal lines run for nine generations, women cluster with relatives in the burial ground, and at least 12 women had children by more than one man. Both draw a family picture: birth mode in a Triassic mammal relative, and who transmitted descent in Iron Age Yorkshire. Each study keeps its limit visible. The bone comes from a single individual and is consistent with live birth rather than proof; the DNA work has not yet completed journal review, and matrilocality is not generalised to south-east England. The week's science rebuilds the family tree in deep time and human archaeology: mammal young may have left the egg earlier than thought, and in one pre-Roman British community the mother-to-daughter line left a more durable cemetery mark than the fathers.[1], [2]
